ESP8266 Smoke Alarm

• ESP8266 Smoke Alarm
  Posted by bob21 on 21 Feb, 2020 11:51
• I am trying to make a smart smoke alarm. Following this:
  
  
  
  
  Before anyone freaks out because a beginner like me is posting this and thinks that I am planning for this unit to replace my main smoke alarms, please do not worry. It will NOT replace the existing mains/battery fitted units, it is supplemental simply for notification. My house has 3 hard wired, communicating alarms that will remain the primary untouched alarms. I am simply trying to add something that will tie into home assistant, for a bit of added protection/notification. Having looked at a handful of ESP designs, this one seems to be the best because the ESP does not drain anything from the 9V battery until the alarm is activated. It is the only design of its kind I came across, all the others require the Kidde relay and mains or a separate lithium cell, or take voltage from the 9V all the time so it drains quicker - so kudos to  Martin Ger for this idea.
  
  I can understand the general idea of the schematic, I just need some help with a few of the components.
  
  A screenshot of the diagram is here:
  
  
   
  
  
  I am unable to get the AMS1117 at CPC, so I am planning to use this: https://cpc.farnell.com/stmicroelectronics/ld1117v33c/ic-v-reg-ld1117-3-3v-to-220-3/dp/SC12896
  
  It looks like the AMS1117 is part of the ESP8266:
  
  
   
  
  
  CPC have the BC547: https://cpc.farnell.com/on-semiconductor/bc547b/transistor-npn-to-92/dp/SC08525
  
  I can find the 68K resistors: https://cpc.farnell.com/multicomp-pro/mcmf006ff6802a50/res-68k-1-600mw-axial-metal-film/dp/RE07819
  
  But what I cannot find is the R580, so am I correct in thinking that I can use 2 x R280's? I am guess the diagram makes reference to the resistance as a whole, as opposed to a particular part, so 2 x this: https://cpc.farnell.com/welwyn/rc55y-280r-0-1/resistor-0-25w-0-1-280r/dp/RE05800
  
  The R280s are on back order though, so any suggestions for that part would be greatly appreciated and indeed any comments/help on the schematic as a whole.
  
  Thanks
• #1 Reply
  Posted by NivagSwerdna on 21 Feb, 2020 12:17
• I like it. 
• #2 Reply
  Posted by bob21 on 21 Feb, 2020 22:06
• Cool
  
  Can I ask for some input on the components? Looks like he has some capacitors on his and he is using a Wifi chip version of the 8266, which I think is this: https://www.ebay.co.uk/itm/ESP8266-ESP-12F-Serial-Wireless-WIFI-Transceiver-Module-Arduino-UK-Fast/273941706452?hash=item3fc832b6d4:g:edQAAOSwnJhdN2rh
  
  I was planning on using CP2102 ESP as it seems to have the AMS1117 built into it, and it's about 26p more. Also (being a beginner) I don't get why there is a diode shown in the wiring diagram before the R580. He obviously isn't a novice, so didn't spell the entire thing out. I don't think people with my limited knowledge are meant to be trying this 
  
  Plus, I think I've made a school boy error in my R280 calc, it would be half the resistance, wouldn't it, so 2 x R280 would be R140. Not R560  I can't find a resistor that is anywhere near R580, so I am assuming this is some other part, possibly related to the diode on the diagram.
  
  Interestingly, someone in the comments has mentioned the SPX3819M5-L-3-0-TR (https://www.mouser.co.uk/ProductDetail/MaxLinear/SPX3819M5-L-3-0-TR?qs=S%2FCBhQS5rCqWy9%252BGPrI6uw==&vip=1&gclid=Cj0KCQiAnL7yBRD3ARIsAJp_oLbvD90ZJt19EDqpMC09F_lgtbB02d2K70A-gVnZQagV3WQy0PlPLgcaAih1EALw_wcB)
  
  

  Quote

  Hello, cool design, just had an empty battery on 1 of my smoke detectors so opened it also to do the same thing ... however I think I can make it even easier with an SPX3819M5-L-3-3 (3.3V LDO with enable pin), the enable pin can be directly tied to port 7 of the smoke detector (it can handle Vin) completly replacing the diode, resistors, the transistor and the  AMS1117 in your design

  
  Could this be the way forward? Hrm, the datasheet states a quiescent current of 90μA so much higher than the original schematic. Maybe not such a good idea.